What is the main topic of this conversation?

M: How did you do on the exam?
W: I passed, but I didn’t do so well. The essay question was the worst part for me. How about you?
M: I did all right on everything except the essay question, too. I wasn’t really prepared to write about the tribes in the rainforests of Brazil. We studied the rainforests for only a few days. I didn’t think it would be on the test.
W: Me either. I thought for sure that he would ask us something about the Incas in Peru or maybe the mountain peoples in Chile. I studied most of the material on these groups and didn’t spend much time on the people of the rainforest. Do you know how much the
exam counts towards our final grade?
M: I think it’s 30 percent.
W: Thirty percent! Oh no, I’m in deep trouble this time! That means I’ll have to get A’s on everything else to get a decent grade.
M: That may not be too hard. We’ve already gone through most of the readings that the class is supposed to cover. After next week it will just be review. But then there is the final paper, of course.
W: Yes. I was hoping to do well on this test so I could relax when writing my paper, but now it looks like I’ll have to spend more time preparing to write that paper.
M: Well, I will too. Hey, I’m kind of hungry. I think I’ll go to get some lunch. Do you feel like joining me?
W: I’d love to, but I have to go home and study. I’ll call you later.